Phenotypic and genotypic characterization of antibiotic-resistant Salmonella spp. isolated from sheep rectal swabs in Tuban, Indonesia

Abstract

Salmonella spp. are important zoonotic pathogens capable of colonizing the intestinal tract of livestock and contributing to the spread of antimicrobial resistance (AMR). This study aimed to investigate the phenotypic and genotypic characteristics of antibiotic-resistant Salmonella spp. isolated from sheep rectal swabs in Tuban, Indonesia. A total of 150 rectal swab samples were collected from sheep and processed using selective enrichment, culture on Salmonella-Shigella Agar, and biochemical identification. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method, while multidrug-resistant (MDR) isolates were further analyzed by polymerase chain reaction (PCR) for the presence of ESBL-associated genes (blaTEM, blaSHV, and blaCTX-M). Out of 150 samples, 20 isolates (13.33%) were confirmed as Salmonella spp. Phenotypic analysis revealed high resistance to erythromycin (100%) and tetracycline (95%), while all isolates were fully susceptible to aztreonam (100%). Moderate susceptibility was observed for ampicillin (80%) and cefoxitin (75%). A total of 5 isolates (25%) were classified as MDR. Genotypic analysis showed that only one MDR isolate (20%) harbored the blaTEM gene, whereas blaSHV and blaCTX-M were not detected in any isolates. These findings demonstrate that sheep can serve as reservoirs of antibiotic-resistant and MDR Salmonella spp., posing potential risks to animal health, food safety, and public health. The detection of blaTEM highlights the presence of β-lactam resistance determinants, although other resistance mechanisms may also be involved. Continuous AMR surveillance, rational antibiotic use, and improved farm biosecurity are essential to mitigate the spread of resistant zoonotic pathogens within a One Health framework.